Plated through hole printed circuit boards

ABSTRACT

PLATED THROUGH HOLE CIRCUIT BOARDS INCLUDE A NONREGISTERED INSULATING SOLDER MASK SUPERIMPOSED ON A CIRCUIT PATTERN CONDUCTOR CARRIED BY AN INSULATING BASE, A HOLE EXTENDING THROUGH THE MASK AND THE CONDUCTOR AND INTO THE BASE, AND A CONTINUOUS METAL DEPOSIT ON THE WALL OF THE HOLE EXTENDING FROM THE BASE INTERIOR TO THE SURFACE OF THE INSULATING MASK AND BRIDGING THE CONDUCTOR.

MGR}! 1974 F. w. SCHNEBLE, JR.. ETAL PLATED THROUGH HOLE PRINTED CIRCUITBOARDS l7 Sheets-Sheet 1 Filed March 27, 1969 FIG"2 FIG- FIG

FIG

INVENTORS. FREDERICK w. SCHNEBLE, JR. JOHN F. McCORMACK RUDOLPH J.ZEBLISKY JOHN DUFF WILLIAMSON JOSEPH POLICHETTE March 26, 1974 w, EB JR"ETAL 3,799,802

PLATED THROUGH HOLE PRINTED CIRCUIT BOARDS Filed March 27, 1969 17Sheets-Sheet a FIG'5 FIG'G FIG-7 FIG-8 FIG-9M FIGIO FIG-ll FIG-l2INVENTORS.

FREDERICK w. SCHNEBLE, JR.

JOHN F. McCORMACK RUDOLPH J. ZEBLISKY JOHN DUFF WILLIAMSON JOSEPHPOLICHETTE March 1974 F. w. SCHNEBLE, JR, E AL 3,799,802

PLATED THROUGH HOLE PRINTED CIRCUIT BOARDS Filed March 27, 1969 17Sheets-Sheet 5 INVEN TORS. FREDERICK W. SCHNEBLE, JR. JOHN F. MCCORMACKRUDOLPH J. ZEBLISKY JOHN DUFF WILLIAMSON JOSEPH POLICHETTE Mal ch 26,1974 F. w. SCHNEBLE, JR. ET AL 3,799,802

PLATED THROUGH HOLE PRINTED CIRCUIT BOARDS Filed March 27, 1969 PEG-8BFIG'QB .FIG-IOB FEG'HB FBGIZB 17 Sheets-Sheet 4 In. I

INVENTORS. FREDERICK w. SCHNEBLE, JR. JOHN F. McCORMACK RUDOLPH J.ZEBLISKY JOHN DUFF WILLIAMSON JOSEPH POLICHETTE M816 26, 1974- w,SCHNEBLE, JR" ETAL 3,799,802

PLATED THROUGH HOLE PRINTED CIRCUIT BOARDS Filed March 27, 1969 17Sheets-Sheet 5 ml INVENTORS.

FREDERICK W. SCHNEBLE, JR.

JOHN F. McCORMACK RUDOLPH J. ZEBLISKY JOHN DUFF WILLIAMSON JOSEPHPOLICHETTE March 26, 1974 F. w. SCHNEBLE, JR. ETAL 3,799,302

PLATED THROUGH HOLE PRINTED CIRCUIT BOARDS Filed March 27, 1969 17Sheets-Sheet 6 FIG-l7 FIG-ITA FlGIQ I FIG'IQA INVENTORS.

FREDERICK w. SCHNEBLE, JR. JOHN F. McCORMACK RUDOLPH J. ZEBLISKY JOHNDUFF WILLIAMSON JOSEPH POLICHETTE March 26, 1974 R w EBLE, JR ETAL3,799,802

PLATED THROUGH HOLE PRINTED CIRCUIT BOARDS Filed March 27, 1969 1,7Sheets-Sheet '7 INVENTORS. FREDERICK w. SCHNEBLE, JR. JOHN F. McCORMACKRUDOLPH J. ZEBLISKY JOHN DUFF WILLIAMSON JOSEPH POLICHETTE Mam}! 1974 F.w. SCHNEBLE, JR. ETAL 3,799,302

PLATED THROUGH HOLE PRINTED CIRCUIT BOARDS Filed March 27, 1969 1,7Sheets-Sheet 8 III/Ill 11/1/11 I FIG-2i lNVENTORS.

JOHN F. McCORMACK RUDOLPH J. ZEBLISKY JOHN DUFF WILLIAMSON JOSEPHPOLICHETTE FREDERICK W. SCHNEBLE, JR.

March 26, 1974 w, EB E, JR" ETAL 3,799,802

PLATED THROUGH HOLE PRINTED CIRCUIT BOARDS Filed March 27, 1969 1'7Sheets-Sheet 9 INVENTORS.

JOHN F. McCORMACK RUDOLPH J. ZEBLISKY JOHN DUFF WILLIAMSON JOSEPHPOLICHETTE FREDERICK W. SCHNEBLE, JR

March 26, 1974 E w SCHNEBLE, JR" ETAL 3,799,802

PLATED THROUGH HOLE PRINTED CIRCUIT BOARDS Filed March 2'7, 1969 17Sheets-Sheet 10 Tfl fi /K K/544114! /Z00 A I M0 l/l/l/l/l/l/l/l IllIII/ll [1/ llll/l l lllq /500 a was l2 2/002 INVENTORS.

JOHN F. MOCORMACK RUDOLPH J. ZEBLISKY JOHN DUFF WILLIAMSON JOSEPHPOLICHETTE FREDERICK W. SCHNEBLE, JR.

March 1974 F. w. SCHNEBLE, JR, ETAL 3,799,802

PLATED THROUGH HOLE PRINTED CIRCUIT BOARDS Filed March 27, 1969 17Sheets-Sheet 11 I000 .II/lllIl/IIII/l/lllllllwlzoa INVENTORS.

JOHN F. McCORMACK RUDOLPH J. ZEBLISKY JOHN DUFF WILLIAMSON JOSEPHPOLICHETTE FREDERICK W. SCHNEBLE, JR.

7 March 26, 1974 w SCHNEBLE, JR ETAL 3,799,802

PLATED THROUGH HOLE PRINTED CIRCUIT BOARDS Filed March 27, 1969 17Sheets-Sheet 12 III/III].-

2200 v if x /500 2200 Z 1l500 Ci I /6 /0 I 0 /000 M0 /0/0 INVENTORS.

FREDERICK W. SCHNEBLE JR. JOHN F. MCCORMACK RUDOLPH J. ZEBLISKY JOHNDUFF WILLIAMSON JOSEPH POLICHETTE March 26, 1974 F. w. SCHNEBLE, JR, ETAL 3,799,802

PLATED THROUGH HOLE PRINTFD CIRCUIT BOARDS Filed March 27, 1969 FIG-2617- Sheets-Sheet 15 INVENTORS.

FREDERICK W. SCHNEBLE, JR.

JOHN F. McCORMACK RUDOLPH J. ZEBLISKY JOHN DUFF WILLIAMSON JQSEPHPOLICHETTE March 26, 1974 w, SCHNEBLE, JR" ETAL 3,799,802

PLATED THROUGH HOLE PRINTFD CIRCUIT BOARDS Filed March 27, 1969 l7Sheets-Sheet 14 I I/I/I/l/I/ INVENTORS. FREDERICK w. SCHNEBLE, JR. JOHNFv McCORMACK RUDOLPH J. ZEBLISKY JOHN DUFF WILLIAMSON JOSEPH POLICHETTEMarch 26, 1974 w, SQHNEBLE, JR" ETAL 3,799,802

PLATED THROUGH HOLE PRINTFD CIRCUIT BOARDS Filed March 27, 1969 1,7Sheets-Sheet 15 INVENTORS.

FREDERICK W. SCHNEBLE, JR.

JOHN F. McCORMACK RUDOLPH J. ZEBLISKY JOHN DUFF WILLIAMSON JOSEPHPOLICHETTE 0; March 197 F. w. SCHNEBLE, JR. ETAL 3,799,802

PLATED THROUGH HOLE PRINTED CIRCUIT BOARDS Filed March 27, 1969 1.7Sheets-Sheet 16 402g A/f/l/l ////////--4 I I-II-IIII 40 I 0 INVENTORS,FREDERICK w SCHNEBLE, JR. JOHN F. McCORMACK RUDOLPH J. ZEBLISKY JOHNDUFF WILLIAMSON JOSEPH POLICHETTE MORGAN, FINNEGAN, DURHAM a PINEATTORNEYS March 26, 1974 w, SCHNEBLE, JR" ETAL 3,799,802

PLATED THROUGH HOLE PRINTFD CIRCUIT BOARDS Filed March 27, 1969 l7Sheets-Sheet 17 INVENTORS, FREDERICK W. SCHNEBLE JR. JOHN F. McCORMACKRUDOLPH J. ZEBLISKY JOHN DUFF WILLIAMSON JOSEPH POLICHETTE MORGAN,FINNEGAN, DURHAM 8 PINE Q ATTORNEYS June 28, 1966, Ser. No. 598,444,Dec. 1, 1966, and

Ser. No. 701,817,.lan. 29, 1968. This application Mar. 27, 1969, Ser.No. 811,142

Int. Cl. H05k 3/00; B41nr 3/08 Us. or. 117-212 7 Claims ABSTRACT OF THEDISCLOSURE Plated through hole circuit boards include a non registeredinsulating solder mask superimposed on a circuit patternconductorcarried by an insulating base, a hole extending through the mask and theconductor and into the base, and a continuous metal deposit on the wallof the hole extending from the base interior to the surface of theinsulating mask and bridging the conductor.

This application is a .continuation-in-part of applications Ser. No.701,817, filed Jan. 29, 1968, Ser. No. 561,123, filed June 28, 1966 andSer. No. 598,444, filed Dec. 1, 1966, each of which now is abandoned.

The foregoing three applications in turn disclose sub ject mattercontained in: 7

Ser. No. 218,656, filed Aug. 22, 1962, now US. Pat. No. 3,259,559,issued July 5, 1966, which in turn discloses subject matter-contained inco-pending application Ser. No. 785,703, filed Jan. 8, 1959, and nowabandoned;

Ser. No. 33,361, filed May 31, 1960, now US. Pat. No. 3,146,125, issuedAug. 25, 1964 which in turn discloses subject matter contained in Ser.No. 831,407, filed Aug. 3, 1959, and now abandoned; and

Ser. No. 26,401, filed May 3, 1960, and now US. Pat. 3,095,309 issuedJune 25, 1963.

This invention relates to new and useful plated through hole printedcircuit boards and more particularly to plated through hole printedcircuit boards having highly reliable solder joints.

: SUMMARY .According to this invention, a non-registered solder mask isused in the manufacture of plated through hole printed circuit boardswith many ensuing advantages.

Heretofore, in producing circuit boards which have a high circuitdensity per unit area, difliculty has been experienced due to the factthat the holes in such boards: (1) tend to have an extremely smalldiameter; and (2) tend to be extremely closely spaced, at least in someportions of the circuitry. In conventional practice, a plated throughhole board is formed with a circuit on one or more exposed surfaces, andthen a registered solder mask is printed over the circuit pattern toleave holes and lands or pads (i.e., small areas on the surfacesurrounding the holes) exposed. Subsequently, the circuit is solderplated as by dipping in a solder bath to plate solder on the lands andin the holes. The mask protects the major portion of the circuit fromthe solder and thus guards against short circuiting by the solder of-theconductor lines making up the circuit pattern.

In such conventional circuits, the lands or pads are exposed whileconductor lines making up theconductor pattern or patterns are protectedby the solder mask.

Accordingly, when the circuit density is high, it" is ex- 3,799,802Patented Mar."26, 1974 tremely vditlicult to print a registered soldermask so as to'provide exposed land or pad areas surrounding the holeswithout some soldering mask accidentally lodging on the .barrel of theholes.

Conventional registered, printed solder masks have other disadvantages.Thus, even'when 'great precautions are taken in printing the solder maskon high density circuit boards of the type described, there is a goodpossibility of. the masks breaking down in part, thereby causing thesolder to bridge from one land to another, or from one conductor line toanother, which in turn results in short circuiting of the finishedboard. Because to maintain fine printing tolerances in such boardsdangerously thin prints are used, the solder mask tends to block theholes, thereby preventing proper soldering. According to this invention,there are providedjplated through hole printed circuit boards which areprotected from solder bridging during assembly and re-working by anon-registered, permanent or temporary solder mask.

In a preferred embodiment, the boards of this invention arecharacterized by plated through holes capable of forming highly reliablesolder joints. The plated through holes comprise lands or pads spacedfrom the plane of the conductor line or lines making up the circuitpattern, at least some of which are in electrical contact with theplated holes.

DETAILED DESCRIPTION An object of this invention is to make rugged,durable and reliable plated through hole printed circuit boards.

A further object of this invention is to make printed circuit, boards,including one-layer, two-layer and multilayer boards, which areprotected from solder bridging during assembly and re-work by anon-registered solder mask.

Afurther object of this invention is to provide printed circuit boards,including one-layer, two-layer and multilayer boards, which are providedwith conductive passageways capable of forming reliable joints with theprinted conductor lines of the circuit pattern.

1 An additional object of this invention is to provid printed circuitboards, including high density one-layer, two-layer and multi-layerboards, which are provided with conductive passageways, or, as morecommonly referred to, plated through holes, characterized by exposedpads surrounding the holes which are non-planar with the conductor lineor lines in electrical contact with the holes.

Still a further object of this invention is to provide printed circuitboards having plated through holes capable of forming reliable solderjoints whose conductors are protected from solder bridging duringassembly and re-work by a non-printed, permanent or temporary soldermask and whose holes comprise pads which are non-planar with theconductor line or lines in electrical contact with the holes.

Other objects and advantages of the invention will be set forth in partherein and in part will be obvious herefrom or may be learned bypractice with the invention, the same being realized and attained bymeans of the instrumentalities and combinations pointed out in theappended claims.

As will be clear from the following description, preferred for use inthe manufacture of the circuit boards of this invention are certaincatalytic blanks and composiice . tions which are inherently receptiveto the deposition of electroless metal and which therefore eliminate theneed for conventional seeding and/or sensitizing solutions, therebyavoiding the problems concomitant with the use of such solutions. Use ofthe catalytic blanks and compositions of this invention insures a strongbond between the laminate foil bonded to the catalytic blank and elec- 3troless metal deposited on the foil, e.g., on

seeder layer is present to interfere with the bond. Also important isthe fact that use of these catalytic blanks and compositions leads tothe achievement of uniformly high bond strengths between the insulatingsubstratum itself and the electroless metal deposit on, for example, theinsulating portion or portions on walls surrounding holes.

Although the catalytic base for the printed circuit boards may take avariety of forms as will be made clear hereinafter, in its preferredembodiment, which will be used to describe the invention, it comprises aresinous material which is catalytic throughout its interior to thereception of electroless metal.

The term catalytic base as used herein generically refers to anyinsulating material which is catalytic to the reception of electrolessmetal, regardless of shape or thickness, and includes thin films andstrips as well as thick substrata. The term catalytic adhesive," alsoused herein, refers to an insulating resinous material with adhe- 'sivecapability which is catalytic to the reception of electroless metal.

The catalytic bases and catalytic adhesives referred to herein arecompositions which comprise an agent which is catalytic to the receptionof electroless metal, i.e., an agent which is capable of reducing themetal ions in an electroless metal deposition solution to metal.

Conductive materials, i.e., metals, may be used as the catalytic agent.Preferred catalytic agents are metals selected from Groups VIII and I-Bof the Periodic Table of Elements, such as nickel, gold, silver,platinum, palladium, rhodium, copper and iridium. Compounds of suchmetals, including salts and oxides thereof, may also be used.

Typical formulations for catalytic insulating adhesives and catalyticinsulating bases suitable for use herein are given in US. Pats.3,259,559 and 3,226,256, the speci fications of which are herebyincorporated herein by reference.

Preferred catalytic agents for dissolution in, dispersion in, chemicalreaction with, or complexing with inorganic or organic materials torender such material catalytic are the metals of Groups VIII and 1-H ofthe Periodic Table of Elements, or salts or oxides thereof, such aschlorides, bromides, fluorides, ethyl acetoacetates, fiuoroborates,iodides, nitrates, sulfates, acetates, and oxides of such metals.Especially useful are palladium, gold, platinum, copper, palladiumchloride, gold chloride, platinum chloride and copper oxide alone or incombination with stannous chloride. J

The catalytic agent, depending upon type, will be-present in amountsvarying from a small fraction, e.g.,- 0.0005 to about 80%, usuallybetween about 0.1 to based upon the combined weight of carrier materialand catalyst. The particular concentration used will depend to a largeextent upon the material used.

The catalytic insulating bases may be prepared by dissolving ordispersing the catalytic agent in an insulating material which may inturn be formed into a three-dimensional object, as by molding. Theresulting article is catalytic throughout its interior to the receptionof electroless metal, so that when holes or apertures are formed -inthethree-dimensional object, the surrounding walls of the holes are alsocatalytic. Thus, when such an article containing apertures extendingbelow the surface is con tacted with an electroless metal depositionsolution, as by immersion therein, electroless metal deposits on thewalls surrounding the apertures, and can be built up to any desiredthickness.

The surface of the insulating catalytic base may or may not becatalytic, depending upon how it is made. The surface could be madecatalytic by mechanical means, as by mild abrasion, e.g., by sandblasting, or by chemical means, as by treatment with chemical solvents,'etchants, milling solutions, and the like. A preferred chemicaltreatment for rendering the surface catalytic and improving bond is totr at the surface with acids or ox diz g g foil edges exposed on wallssurrounding holes, since no intermediate e.g., nitric and chromic acids,permanganates and the like. Alternatively, the exposed surface orsurfaces of the catalytic bases could be made catalytic by coating themwith a thin film of the catalytic adhesives or inks of the typedescribed herein.

In another embodiment, an insulating resinous material having acatalytic agent dispersed therein, or dissolved therein, or reacted orcomplexed therewith, is used to impregnate laminae of paper, wood,Fiberglas, polyester fibers and other porous materials. These base materials, for example, are immersed in the catalytic resin or the catalyticresin is sprayed onto the base material, after which the base materialsare dried in an oven until all the solvent has evaporated. The laminaeare then bonded together to form a base of any desired thickness,thereby providing a lamina of the type described impregnated with thecatalytic resin.

A further alternative is to pre-form or pre-mold thin films or strips ofunpolymerized resin having dissolved in or dispersed in or reacted withor complexed with a catalytic agent, and then laminate a plurality ofthe strips together to form a catalytic insulating base of the desiredthickness. In each embodiment, the interior of the insulating base willbe catalytic throughout, such that, when holes or apertures are formedtherein at any part, the walls of the holes or apertures will besensitive to the reception of electroless metal from an electrolessmetal chemical deposition solution such as an electroless coppersolution.

In making catalytic bases of the type described, wherein the catalyticagent is dissolved or dispersed in the resin, it is helpful if thecatalytic agent is initially dissolved in a suitable solvent prior toincorporation into the resin. The solvent may then be evaporated duringcuring of the resin.

In another embodiment, a solution of the catalytic agent could be usedto treat an adsorbent filler to thereby impregnate the filler with acatalytic agent. The catalytic filler could then be incorporated intothe base or carrier material. Typical fillers are those ordinarily usedin resins and plastics. As examples may be mentioned aluminum silicate,silica gel, clay, such as kaolin, attapulgite, and the like.Alternatively, a base exchange resin or clay, including crystallinealuminosilicate, could be base exchanged with an aqueous or organicsolution of a catalytic agent in the form of a salt, and the exchangedresin or clay or crystalline aluminosilicate incorporated into the resinbase.

' organic clays or minerals prior to firing.

As already brought out, the term catalytic as used herein refers to anagent or material which is catalytic to the reduction of the metalcations dissolved in electroless metal deposition solutions of the typeto be described.

Amongthe organic materials which may be used to form the preferredcatalytic insulating bases and adhesives described'herein may bementionedthermosetting resins, thermoplastic resins and mixtures of theforegoing.

Among the thermoplastic resins may be mentioned the acetal resins;acrylics, such as methyl acrylate; cellulosic resins, such as ethylcellulose, cellulose acetate, cellulose propionate, cellulose acetatebutyrate, cellulose nitrate,

and the like; chlorinated polyethers; nylon; polyethylene;polypropylene; polystyrene, styrene blends, such as acrylonitrilestyreneco-polymers and acrylonitrile-butadienestyrene co-polymers;polycarbonates; polychlorotrifluoroethylene; and vinyl polymers andco-polymers, such vinyl acetate, vinyl alcohol, vinyl .butyral, vinylchloride, vinyl chloride-acetate co-polymer, vinylidene chloride andvinyl formaL. T Among the thermosetting resins may-be mentioned allylphthalate; furane; melamine-formaldehyde; phenol formaldehyde andphenol-furfural co-polymer, alone or com pounded with butadieneqacrylonitrile co-polymer or acrylonitrile-butadienestyreneco-polymers;polyacrylic esters; silicones; urea formaldehydes; epoxy resins, allylresins; glyceryl phthalates; polyesters; and the like.

The catalytic adhesives will ordinarily comprise a flexible adhesiveresin, alone or in combination with thermosetting resins of the typedescribed. Typical of the flexible adhesive resins which may be used insuch a system are the flexible adhesiveepoxy resins, polyvinyl acetalresins, polyvinyl alcohol, polyvinyl acetate, and the like. Preferredfor use as the adhesive resin are natural and synthetic rubber, such aschlorinated rubber, butadiene acrylonitirle co-polymers, and acrylicpolymers and co- Example 1 Butyrolactone grams 60 Palladium chloride do0.1 Concentrated (37%) hydrochloric acid.. drops 5 a The composition ofthis example is added to an epoxy resin-hardener system, and the systempermitted to cure to form a resin base whose interior is catalytic'tothe reception of electroless metal.

Example 2' v N-methyl-Z-pyrrolidone grams 50 Palladium chloride do 0.5Diacetone alcohol milliliters s50 Prolonged agitation is required toassure complete solution of the palladium chloride. The resultingsolution may be added to a variety of thermoplastic and thermosettingresinous base materials and also used toimpregnate glass cloth.Following evaporation of the solvent, lamination and/or curing, theresulting bases will be found to be catalytic to, the reception ofelectroless metal.

Other preferred embodiments of catalytic solution which can be added toresins to produce catalytic bases include: t

' TABLE Palladium choride in tetrahydrafuran Palladium chloride indimethyl sulfoxide Palladium chloride in dimethyl sulfoxide andmethylene" chloride Palladium chloride in dimethyl formamide Palladiumchloride in Cellosolve acetate Palladium chloride in methylethyl ketonePalladium chloridein xylene Palladium chloride in acetic acid IPalladium chloride in tetrahydrofurfuryl alcohol. Palladium chloride inmethylene chloride Gold chloride in ethyl alcohol 7 Chloroplatinate inethyl alcohol. i

Of the catalyst solutions listed 'the table', particularly stable forlong periods of time isa solution of 10% palladium chloride in a mixtureof dimethyl sulfoxide and methylene chloride.

As .will be clear from the foregoing, the catalyst solutions of the typedescribed in Examples 1 and 2, and in the table, inadditionto beinghighly useful for addition to. thermosetting or thermoplasticresincontaining systems to catalyze the 'same, are also suitable forimpregnating-coating materials, such as paper and glass cloth containingresinous laminates and the like, to render such compositions catalytic.These catalytic solutions may also, for example, be used in combinationwith solid catalytic agents, e.g., metals and metal oxides of Groups 1and 8, to make systems containing solid, dispersed catalytic agents moreresponsible to electroless metal deposition.

The catalytic insulating adhesives of this invention are used to bondlayers of material together so that the interface is catalytic toelectroless metal deposition. In use, the surfaces of the material to'be bonded need only be immersed in or sprayed with the catalyticadhesives, following which the solvent may be evaporated as by heating,to deposit on the substrate a flexible adhesive resin containing thereinthe catalytic agent. Typical systems of this type are described inExamples 3 to 5.

Example 3 1312) 20 Phenolic resin (SP 103) 20 Phenolic resin (SP 126) 20Phenolic resin (SP 6600) 20 Acrylonitrile butadiene (Paracil CV) 144Silicon dioxide (Cab-O-Sil) 50 Wetting agent (Igepal 430) 17.5

Separate solutions of the following salts were prepared at roomtemperature:

Palladium chloride Cupric chloride Silver nitrate Auric chloride.

- The resulting solutions were mixed with an equal part byweight, of theadhesive binder. Each of the resulting adhesive resin systems may beused to bond insulating and/or conducting laminae together so as toprovide a bond interface which is catalytic to the recepton ofelectroless metal.

1 Example 4 I Grams N-methyl-Z-pyrrolidone 50 Auric chloride 1.67Adhesive 10 300 Example 5 Grams N-methyl-Z-pyrrolidone 50 Palladiumchloride 1 Stannous chloride 1.13 Adhesive l0 300 i Example 6 J Gr mN-methyl-Z-pyrrolidone 40 Auric chloride 1.67 Stannous chloride T 1.13Adhesive 10 300

